Policy

static

Defines an Identity and Access Management (IAM) policy. It is used to specify access control policies for Cloud Platform resources.

A Policy consists of a list of bindings. A Binding binds a list of
members to a role, where the members can be user accounts, Google groups, Google domains, and service accounts. A role is a named list of permissions defined by IAM.

etag is used for optimistic concurrency control as a way to help prevent simultaneous updates of a policy from overwriting each other. It is strongly suggested that systems make use of the etag in the
read-modify-write cycle to perform policy updates in order to avoid race conditions: An etag is returned in the response to getIamPolicy, and systems are expected to put that etag in the request to setIamPolicy to ensure that their change will be applied to the same version of the policy.

If no etag is provided in the call to setIamPolicy, then the existing policy is overwritten blindly.